Glue can be applied to a rapidly moving web, e.g. in a high-speed printing press using an applicator cylinder or drum in which a substantial region of the outer surface of an applicator cylinder driven rotatably about its rotation axis is contacted by the web to which adhesive is to be applied and the corresponding areas of that outer surface are dimensioned according to the spacing of the transverse adhesive portions or lines to be applied to the web.
The adhesive material from a fixed axial supply duct is conducted to an adhesive glue feed duct rotating with the applicator cylinder which extends to a line on the outer surface of the applicator cylinder along which a plurality of outlet openings in the applicator cylinder are provided for the adhesive or glue.
An adhesive application operation with these features is taught in German Pat. No. 32 22 335. The portions of adhesive are applied to a very rapidly running paper or fabric web with rotating applicator cylinder on whose periphery along a line on the outer surface there is an array of outlet openings for the adhesive. The adhesive material is delivered pointwise through these openings. The transverse line of adhesive on the web thus is now of glue spots at these points.
On account of the high speed of the web to which adhesive is to be applied the applicator cylinder necessarily has a high rotational speed. This leads to problems in the discharge of adhesive material from the outlet openings. In order to prevent centrifugal force from discharging glue improperly, the outlet openings are closed from the inside when these outlet openings are not covered by the web to which adhesive is to be applied.
On the other hand, the web is fed with a comparatively large contact angle around the applicator cylinder. Where the web contacts the applicator cylinder the outlet openings are opened from the interior so that the adhesive material can be conducted to the web under the influence of centrifugal force. When the applicator cylinder and apparatus is at rest sealing rollers press against the outlet openings from the outside of the applicator cylinder.
The applicator of German Pat. No. 32 22 335 has achieved widespread acceptance in the printing industry. Particularly in gavure printing. However problems arise which are associated with the different lengths of the printed page. The printing machine is usually formed so that the entire printing cylinder can be interchangeable with another of a different diameter so that the machine can print the web with pages of different length.
The applicator cylinder for the adhesive must have a completely defined diameter and the required spacing of the portions of adhesive on the web is constant. However, should the need arise for a size change in the gravure machine not only must the gravure printing cylinder be changed, but the entire glue applicator cylinder must be correspondingly replaced. The same problem occurs also with other machines in which the spacing of the transverse adhesive portions must be changeable.